Re: [REGRESSION][BISECTED] tun/tap & vhost-net: multi-threaded network performance

[Michael S. Tsirkin]

On Fri, Jul 03, 2026 at 12:41:19PM +0200, Simon Schippers wrote:
> On 7/1/26 21:16, Brett Sheffield wrote:
> > TL;DR - Commit 1d6e569b7d0c0b2736636749e4be0a27f3cefcb3 causes
> > significant performance regressions with TAP interfaces and multithreaded
> > network code. Please revert.
> 
> Micheal, I am convinced that netdev_tx_stop_queue() and
> netdev_tx_wake_queue() are too slow. The communication between the CPUs
> is just too slow. We already spent *a lot* of time speeding it up, the
> patchset was only merged at v12...
> 
> Yes, I would *love* to have qdisc backpressure on by default but I do
> not see how anything could speed it up.
> 
> 
> *Is there any issue if we introduce IFF_BACKPRESSURE?*
> I implemented it and it is a simple patch that only executes the
> stopping / waking  if ((tun->flags & IFF_BACKPRESSURE)).
> I could submit that to [net] very soon.
> 
> Thank you,
> Simon

Pls go ahead.

-- 
MST